This application claims priority from European Patent Application No. 98 121 033.9 filed Nov. 5, 1998.
The invention relates to a method and an apparatus for shrinking a foil onto an object as defined in the preamble of claim 1 and/or the preamble of claim 10. Such a method and/or such an apparatus mostly are used for packaging objects which are packaged prior to further transport in order to protect them against environmental influences and to increase stability of the packaged object.
Generally plants for packaging objects are known in which a shrinking means essentially is formed by an annular shrink frame on which a plurality of heating elements, like gas burners, electroheater bodies or the like, is arranged. For packaging an object, the shrink frame is laterally moved along an object over which a foil hood was pulled. Therein, for shrinking said foil hood the heating means is switched on and the shrink frame is moved along said foil hood in vertical direction such that the foil hood shrinks under the influence of heat and bears on the object.
An essential disadvantage lies in that in case of packagings which are unfitted or are provided with different foil thicknesses varying heat charge of the sides of the packaging occurs, as also is the case with packagings not having a basic area of axial symmetry.
As furthermore the shrink frame is not build rigidly, by the known apparatus only an object of uniform size can be packaged, since in case of smaller objects the distance to the heating means becomes to large for reaching the shrinking temperature and in case of an object which is to big, the distance to the heating means is to small such that holes are created in the foil or the foil even can be ignited. The uniform energy supply in addition has the further disadvantage that the energy consumption in unnecessarily high as it cannot be adapted to the individual demands during shrinking of a foil onto an object.
It is, therefore, the object of the present invention to create a method and apparatus for shrinking of a foil onto an object, in which the energy consumption is minimized and objects of different sizes in particular can be provided with a shrunk-on fail.
This object is solved with a method with the features of claim 1 and with an apparatus with the features of claim 10. Preferred embodiments of the invention are cited in the subclaims.
In accordance with the method according to the present invention, at least sectionally the temperature of the foil is measured for regulating the heat emission from the heating means to the foil. This permits an individual adaptation of the energy supply during shrinking such that in case of low heat demand for shrinking the foil, energy supply can be reduced and thus the all-over energy consumption of the apparatus is reduced. In addition, by the regulation of the heat emission to the foil the latter can be arranged at different distances with respect to the heating means such that objects of different sizes can be provided with a shrunk foil. In particular, objects with an irregular lateral surface can be provided with a shrunk-on foil better, as in protruding areas heat emission is reduced and in areas recessed with respect to the heating means heat emission can be increased. The advantage of the adjustable heating means additionally lies in that not only different objects can be covered with a shrunk foil but that the apparatus can adapt itself to the position of the object in relation to the heating means. It even is possible also to cover an object not arranged centrally with respect to the heating means, with a shrunk foil without problem, Furthermore, the method can be used for different foil thicknesses or foil materials, as the heat supply respectively is optimally adjustable to the foil. The regulation of the heat emission of the heating means therein permits an energetically optimized shrinking method independently from the ambient temperature and other environmental influences.
In accordance with a preferred embodiment of the method in accordance with the present invention as defined in claim 1, the temperature to be reached, of the foil essentially is adjusted to a range somewhat above the shrinking temperature in order to minimize energy consumption during shrinking and simultaneously guaranteeing efficient shrinking.
Preferably, heat emission of the heating means is regulated by the temperature of the latter. Alternatively, however, also the speed of the heating means in relation to the foil or the distance of the heating means to the foil can be regulated. The individual parameters can also be regulated in combination with one another.
If, e.g. the object essentially is of ashlar shape, it is possible in a preferred embodiment of the invention to measure the temperature at least in the central area of each lateral surface. In case of objects of ashlar shape the foil surrounding the object arches to the outside in the central area such that in the central area the distance to the heating means is smallest. For safety reasons, therefore, at least in the central area a temperature measurement means should be provided for in order to avoid creation of holes or ignition of the foil.
A simple realization of regulation of heat supply can be achieved, when the heating means consists of several gas burners and regulation of the heat emission is effected by regulation of the volume flow of the gas.
In accordance with the apparatus according to the present invention a means for measuring the temperature of the foil and a means for regulating The temperature of the foil are provided for such that the heat emission of the heating means during shrinking can be optimally regulated in correspondence with the respective demands. In particular, the constructional additional expenses due to the additional means are kept into warrantable limits.
Preferably, heat emission of the heating means can be regulated by the means for regulating the temperature of the foil, wherein alternatively or additionally also the speed of the heating means with respect tot he foil or the distance of the heating means to the foil can be adjustable. The apparatus can be adjusted to the demands in most flexible manner, if the temperature as well as the speed and the distance can be regulated.
Preferably, the means for measuring the temperature includes several measuring units which each are arranged in the central area of the lateral surfaces of shrink frame e.g. annularly surrounding a good to be packaged. In an ashlar object the distance to the heating means is smallest in the central area, since the foil in this area arches away from the object. Furthermore, an air cushion exists between the foil and the object such that this area is particularly suitable for shrinking without heating the object itself.
An individually controllable heating means includes several gas burners and/or electroheating bodies, infra-red radiators or the like, which are arranged in or on a shrink frame. By the individual control of the heat emission of the individual heater bodies an almost equal temperature can be achieved at the lateral surfaces of the object to be packaged even if these lateral surfaces e.g. have a varying distance to the heater bodies due to an irregular contour of the object, Even a change of the contour over the height of the object to be packaged does not cause a change in the shrinking temperature of individual foil areas. Thus, also an accurate adjusting of the object to be packaged with respect to the shrink frame is no longer required.
Preferably, a cooling blower means for cooling the foil is arranged adjacent to the heating means such that the cooling blower means can blow away a rising stream of heated air which maybe could falsify the measuring results, A particularly simple and reliable means for measuring the temperature of the foil is an infra-red measurement means.